Regardless of whether audio is a primary aspect of your app’s experience, you need to know how people expect audio to behave and meet those expectations.
Transition to the Now Playing screen only when content is ready to play. Due to buffering and network conditions, it may take several seconds for audio to begin playing after a user selects it. The user’s selection remains highlighted, and a spinning activity indicator is displayed until your app informs the system that the audio is ready to play.
Start playback as soon as audio has sufficiently loaded, even if descriptive information is still loading. Continue loading descriptive information in the background, and show it once it's available.
Avoid beginning playback automatically. Unless your app’s purpose is to play a single source of audio, or your app is resuming previously interrupted audio, it shouldn’t begin playback until the user initiates it.
Resume audio playback after an interruption only when it's appropriate. Temporary interruptions such as incoming phone calls are resumable. Permanent interruptions, such as a music playlist initiated by Siri, are nonresumable. When a resumable interruption occurs, your app should resume playback when the interruption ends if audio was actively playing when the interruption started.
Adjust levels automatically when necessary, but not the overall volume. Your app can adjust relative, independent volume levels to achieve a great mix of audio. However, the final output volume should always be controlled by the user.
Use the system’s sound services for short sounds, such as a sound accompanying an alert. For developer guidance, see System Sound Services.
If your app is an audio app, see Audio Apps for related design guidance.